Method and apparatus for synchronizing multiple transmitters

Abstract

A method and apparatus for synchronizing multiple transmitters is disclosed. A global time reference is used to synchronize the arrival of data from a plurality of secondary transmitters in a receiver station. In one embodiment, the global time reference is provided by a GPS satellite, and may also be used to synchronize the carriers of the signals received at the receiver station from each of the plurality of transmitters. In one embodiment, a pilot signal used for ATSC applications is added by the secondary transmitters.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a continuation in part of U.S. patent application Ser. No. 12 / 947,604, entitled “METHOD AND APPARATUS FOR SYNCHRONIZING MULTIPLE TRANSMITTERS,” by Robert E. Wetmore, filed Nov. 16, 2010, which application is hereby incorporated by reference herein.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention relates to systems and methods for wireless transmission, and in particular to a system and method for synchronizing transmissions from multiple transmitters.[0004]2. Description of the Related Art[0005]Terrestrial transmission systems have been used for many years to transmit television signals to television sets and other home based receivers. It is desirable for the range and scope of such television transmissions to be well controlled to assure that the television signals are receivable by the maximum number of appropriate viewers. At the same time, such transmissions must prevent interf...

AI Technical Summary

Benefits of technology

"The present invention provides a method and apparatus for transmitting media program information. The technical effect of this invention is that it allows for the efficient and reliable transmission of media program information to a remote receiver station in a coverage area of multiple secondary transmitters. This is achieved by generating a first signal with the media program information and synchronization information, transmitting it from a master transmitter, receiving it in the first and second secondary transmitters, and transmitting retransmitted signals from each secondary transmitter with a temporal offset based on the synchronization information and a common time reference. This ensures that the media program information is received correctly and without interference between the retransmitted signals."

Problems solved by technology

However, even when optimally placed, such primary transmitters often cannot provide a strong enough signal to areas that are shadowed by natural features such as mountains and / or blocked or reflected by with by man-made features such as buildings and other transmitters.

One difficulty in the use of such auxiliary transmitters is that the signals that they transmit may interfere with the signals broadcast by the primary transmitter or other transmitters.

However, even using such techniques, the coverage area of the transmitters may overlap, raising the specter of interference in those areas.

While the '048 patent proposes a solution to the interference problem, it does not disclose a system that ensures that the data received from a first repeater is completely identical to data received from the main transmitter.

If the data received from a first repeater is not identical to that received from the main transmitter regardless of the time delay, the non-identical data will cause mutual interference.

Additionally because the described processing adds potentially different time delays to each of the signals from each transmitter, the '048 patent makes no provision for assuring that the data transmitted by each transmitter is received within the ability of a receiver to equalize out the resultant intersymbol interference.

While some of the receivers can equalize out the effects of echoes, they cannot correct for interference.

Further, at some point, the delays may be large enough to exceed the capacity of the equalizers to detect and cancel the echoes.

Accordingly, the system disclosed in the '048 patent will result in transmissions that cannot be received due to interference or excessively long echoes.

Another problem is that after demodulation, the data itself from the different transmitters 104 do not arrive at the receiver station 108 at the same time, thus causing reception difficulties.

Channel equalizers in the receiver stations 108 can ameliorate the echoed data to a certain extent, but at some point, the channel equalizers become ineffective, and the echoed data begins to compromise reception of the signal to the point where the data arriving later from other transmitters essentially becomes interference, and resulting data is unusable.

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